The present invention relates to radiation delivery systems, and, in particular, to a radiation delivery balloon in which the radiation source is carried in the wall of the balloon.
Percutaneous transluminal coronary angioplasty ("PTCA") has become an established treatment for occlusive coronary artery disease. A catheter having an inflatable balloon secured to its distal end is advanced through an artery to a narrow region. The balloon is then inflated with a fluid from an external source, causing the narrowed region of the artery to be expanded. The balloon is then deflated and withdrawn. A variety of additional techniques have been developed for restoring patency to a narrowed vessel, including, for example, laser angioplasty and rotational arthrectomy. Although such techniques have enabled a minimally invasive treatment for patients who may otherwise would have been subjected to open heart surgery, long-term follow-up shows that a renarrowing of the vessel or restenosis frequently occurs.
Several studies document a restenosis rate of from about 25% to as much as 35% or more within the first year following PTCA, with the vast majority of patients requiring repeat procedures within six months. In addition, the restenosis rate for angioplasty of the smaller, peripheral arteries also occurs at a significant rate.
Immediate restenosis, also known as abrupt reclosure, results from flaps or segments of plaque and plaque-ridden tissue which are formed during balloon angioplasty and which can block the artery. Such blockage of the artery requires emergency surgery and often results in death. Furthermore, the possibility of an acute reclosure may require that a surgical team stand by during the balloon angioplasty procedure. Restenosis at a later time results from causes that are not fully understood. One mechanism believed responsible for restenosis is fibrointimal proliferation of the stretched wall in which the injured endothelial cells lining the vascular structure multiply and form obstructive fibrous tissue. Fibrointimal proliferation of the vascular wall involves cellular multiplication at a high rate, thereby causing an obstruction to flow through the vascular structure. Often repeat balloon angioplasty or surgery is required, and another episode of restenosis may occur.
At present, there is no effective method for preventing restenosis following angioplasty, arthrectomy, or any of the variety of additional lesser used techniques for restoring patency to a vascular stenosis. However, a variety of techniques have been explored for minimizing restenosis following angioplasty.
For example, a variety of catheters have been devised for delivering heat to the artery wall. See, for example, U.S. Pat. Nos. 4,878,492 and 4,646,737 to Hussein, et al., which are directed to the use of a laser as the heat source.
More recently, exposure of the dilated vascular site to a radioactive source has appeared to show more promise in inhibiting or delaying restenosis. As a consequence, a variety of radiation delivery vehicles have been designed.
For example, radioactive stents and radioactive guidewires are disclosed in U.S. Pat. No. 5,213,561 to Weinstein, et al. A variety of other radioactive catheter structures have also been devised, such as, for example, that disclosed in U.S. Pat. No. 5,199,939 to Dake, et al.
Notwithstanding the various efforts in the prior art to devise an effective radiation delivery system, the systems devised so far contain certain disadvantages. For example, delivery of a uniform dose of radiation circumferentially around the artery is difficult with the radioactive guidewire-type delivery systems, unless the guidewire is centered within the artery such as through the use of a balloon catheter. With the centered guidewire, the radiation dose must be sufficiently high to penetrate the centering catheter and blood or inflation media before penetrating the arterial wall. Radioactive stents may be able to provide a more circumferentially symmetrical delivery of radiation, but removal of an implanted stent is difficult or impossible as a practical matter. Thus, the clinician can exert relatively little control over the dosage delivered through such devices.
Thus, there remains a need for a radiation delivery vehicle for delivering a predetermined dosage of a low energy radiation to a site for a conveniently controllable period of time, for minimizing or delaying restenosis or other proliferative conditions.